Hi there Fodorites. The information on these forums is always very helpful. I am planning a solo trip to Spain in early June and this is where I anticipate visiting, all by way of trains and buses. I would be flying in to Barcelona and then head up to San Sebastian and over to Bilbao and then Madrid with a trip to Toledo. Is this too much to do?

No, not too much IMO - can take overnight train to S S from Barcelona to save daytime travel time. Trains great all those routes - S S t Bilboa bus may be better. Anyway for lots on Spanish trains (where you time the Pain in Spain was largely on the train it is not now as Spain has thoroughly modernized its rail system) - check Renfe - Spansih Railways site -book early forpossible discounts; www.seat61.com; BETS-European Rail Experts and www.ricksteves.com.

Toledo is an easy day trip from Madrid by train.

Flying from Barcelona to Bilbao takes 1hr 15min in the air. Adding a couple of hours at the Barcelona airport is still much faster than taking the train, and for about the same price flying Vueling. You can then take the bus to Donostia-San Sebastian after spending some time enjoying Bilbao. There is no overnight train on the Barcelona-San Sebastian or Bilbao routes, just a late afternoon train.

19 days minus travel days

Barcelona 5 nights
maybe day trips like to Montserrat (popular pilgrimage mecca on mountain top near Barcelona - easy by train and cable car to top

night train to S Seb (change in Burgos) or fly to S S

5 nights

Bilboa 2 nights

Madrid - lots of neat day trips - Toledo of course; Salamanca (neat overnight as would be Toledo), Avila, Segovia for starters.

So you can see that is not too much but for some too little!

It really depends on what you want to see and experience, but with 2.5 weeks, I would think you could come up with a do-able plan. I wouldn't try to fit in all the places PalenQ mentions, you certainly have a lot of options.

If you haven't already seen it, you might find some useful information in the report of my solo visit to Catalunya and parts of northern Spain:
Four Awesome Weeks in the North of Spain and Catalunya

Hope that helps!